Pureline Selection – Procedure, Applications, Advantages, Disadvantages

Pureline selection is a method used in plant breeding where plants are chosen from a single self-pollinated variety to create a population that is genetically uniform.

It was first introduced by Johannsen (1903) while working with beans (Phaseolus vulgaris).

The method based on assumption that variation seen in self-pollinated crops is mostly due to environment not genetics.

In this selection, a single plant with desirable traits is selected and its progeny (offspring) are grown separately.

Each progeny line (called pure line) is evaluated for yield, quality, disease resistance etc.

After that, the best pure line is maintained and multiplied for future cultivation.

Pureline selection gives high uniformity, but also leads to less adaptability because genetic variation reduced drastically.

This technique works mainly for self-pollinated crops like wheat, rice, barley, etc.

It is a slow process, sometimes taking 8–10 years for stabilizing the line properly.

The selected pure line is genetically identical — that means, no segregation occurs in later generations.

Advantage – easy to maintain uniformity & quality. Disadvantage – poor adaptability under changing environment.

So, Pureline selection mainly used when stability & uniform product quality is more important than variability.

The idea of pure line selection came from work by Johannsen (1903) on beans (Phaseolus vulgaris), where he grew many lines from single self-pollinated plants.

His experiment showed that variation among plants of one selfed line was caused by environment, not by genetic difference.

Before his research, breeders thought that visible differences inside one variety could be improved by selection within that population.

Johannsen proved that, after self-pollination for many generations, each line becomes genetically uniform – what he called a “pure line.”

This finding changed earlier methods of mass selection, which mixed both genetic + environmental effects together.

The term Pure Line Selection was later used widely for self-pollinated crops like wheat & barley to fix desirable characters.

During 1920s–1930s, plant breeders in Europe and India applied this method for stabilizing varieties with higher yield and disease resistance.

It became standard approach in breeding stations — for example, early Indian wheat programs used pureline selection to isolate lines from Punjab wheat populations.

The method dominated till hybridization methods grew popular after 1940 when breeders wanted new variability.

Still, pureline selection remained vital for maintenance breeding and for releasing stable seed stocks that perform uniformly.

In later decades, this concept merged with modern genetic purity testing using molecular tools (though idea itself remained same).

Definition of Pureline Selection

Pureline selection is a plant breeding method where individual plants are selected from a self-pollinated crop, and their progeny are evaluated. The best-performing progeny, derived from a single homozygous plant, is released as a pureline variety, ensuring genetic uniformity.

Characteristics of Pureline Selection

• Pureline means the plants are derived by continuous self-pollination from one selected individual.
• The population is genetically uniform, so almost all plants look same under similar environment.
• Any variation seen inside a pureline mostly caused by environmental effects, not heredity.
• Every plant in pureline supposed to have identical genotype, therefore, no segregation occurs in later generations.
• The heritability within a pureline is practically zero – since genetic variance already removed.
• Selection within such line is ineffective, because all individuals carry same genes.
• High uniformity in growth, maturity and yield makes it useful for commercial cultivation.
• However, this uniformity also reduce adaptability under changing or stress environments.
• Purelines are homozygous and homogeneous (terms sometimes mixed up / used loosely by workers).
• Maintenance breeding becomes easy since line remains true to its type generation after generation.
• Usually applied in self-pollinated crops like wheat, rice, barley, gram, etc.
• Because of absence of heterozygosity, once a line is fixed – it stays stable for long time, unless mutation or contamination happen.
• Such uniformity helps in quality control, seed certification and standardization of products.
• In pureline selection, the genetic base is narrow, yet that’s exactly what gives predictability of performance.
• It’s a steady / reliable method though slower, sometimes breeders call it a “patient approach” (small humor but true).

Procedure of Pureline Selection

Step One – Selection of Individual Plants (First Year)

• About 200–3,000 plants are picked from a mixed or local population.
• Each plant harvested separately to keep its genetic identity distinct.
• Selection done with enough spacing so every plant can be judged alone.
• Criteria: flowering time, maturity, disease resistance, plant height, awns presence, grain type etc.
• Larger sample size preferred (within land/time/resource limits) because more plants mean better chance to catch useful ones.
• The goal here is – collect possible superior genotypes for later study.

Step Two – Evaluation of Progenies (Second Year)

• Seeds from each selected plant sown separately in rows or plots.
• Progenies checked visually for plant type, height, grain form and disease resistance.
• Lines showing excess segregation or poor growth are rejected.
• Often, artificial disease conditions created to check resistance (esp. rust, smut etc.).
• This step reduce number of lines and keep only the promising progenies.

Step Three – Yield Trials (Third Year)

• Surviving progenies entered in replicated yield trial, with a check variety for comparison.
• Traits noted: yield, resistance, maturity, and general appearance.
• Sometimes a preliminary yield trial arranged if seed quantity already enough.
• The best few progenies selected, each one considered a pureline, so no further within-line selection required.

Step Four – Advanced Yield Trials (Fourth Year)

• Selected lines tested again under replicated trials using the top commercial variety as reference.
• Close observation taken for flowering time, maturity, and disease behavior.
• Quality tests done for grain size, color, cooking or milling quality, etc.
• Best strains promoted to next multi-location testing stage.

Steps Five to Eight – Multi-Location Trials (Fifth–Eighth Years)

• Promising strains tested at several research centers or regional stations.
• These trials check stability of yield and adaptability in different soils, climates.
• The new lines compared against already released varieties from other breeders.
• Data collected for performance, disease score, and reaction under diverse field conditions.

Step Nine – Release of New Variety (Ninth Year)

• The line showing consistent superior performance across years and locations is proposed for release.
• Official variety release based on full evaluation data – yield, quality, resistance and stability records.
• After approval, breeder seed produced and distributed for multiplication.
• The selected pureline then becomes a new commercial variety, maintained through self-pollination in future seed programs.

Use of Pureline Selection

• Used mainly for self-pollinated crops like wheat, rice, barley, gram, and oats, where uniformity is needed.
• Employed to develop new pure varieties from old local or mixed populations that show variation in field.
• Applied when the goal is to improve a landrace without creating new genetic combination by hybridization.
• Used in maintenance breeding to keep breeder seed genetically clean and true-to-type every season.
• Helpful for restoring purity of an old released variety that has become mixed or contaminated.
• Commonly practiced in quality improvement programs – for example to isolate pure strain with better milling, cooking, or baking properties.
• In early breeding stations (esp. India & Europe) it was used to identify high-yielding lines from landraces; those lines later released as standard cultivars.
• Used in teaching & research, to study inheritance of simple traits because purelines give clear genetic background (no segregation).
• Plays role (small but steady) in seed certification, as foundation stock often comes from pureline derived variety.
• Sometimes combined with mutation breeding, so that the mutant line selected further purified through pureline selection steps.
• Useful where stability is valued more than adaptability – such as regions with uniform environment or controlled irrigation.
• Even today, used to preserve traditional varieties, helping farmers maintain uniform type for niche or heritage crops.

Applications of Pureline Selection

• Ensures Genetic Uniformity– All plants in a pureline are almost identical genetically, so crops show even growth and yield under same field conditions.
• Improves Local Landraces– Used to extract the best performing strain from a traditional population without hybridization effort.
• Maintains Variety Purity– In seed programs, pureline selection is applied for maintaining breeder seed true-to-type through self-pollination cycles.
• Restoration of Old Varieties– Helps to purify and recover lost or mixed characters in older cultivars.
• Used for Quality Improvement– isolates uniform lines showing better grain texture, cooking / milling or industrial quality.
• Useful in Research Work– provides stable genetic background for inheritance and physiological studies because no segregation appears in progenies.
• Applied in Teaching Programs– students use pureline crops to understand variability, heritability and selection response concepts.
• Foundation for Seed Certification– pureline varieties often serve as base stock for seed multiplication and certification systems.
• Stable Performance– since plants are homozygous and homogeneous, they perform reliably in uniform environment (though adaptability less).
• Economic Importance– farmers get predictable yield and quality; industries prefer such uniform lots for processing convenience.
• Used with Mutation Breeding– mutants isolated further purified by pureline selection to develop new fixed varieties.
• Preservation of Traditional Crops– keeps native types stable for niche markets and biodiversity conservation.

Advantages of Pureline Selection

• High Genetic Uniformity– all plants of a pureline look and behave nearly same, which simplify field operations & harvesting.
• Stable Performance– yield and quality remain steady year after year under uniform environment.
• Easy Maintenance– breeder seed of a pureline can be maintained easily since self-pollination keeps it genetically fixed.
• Restoration of Purity– old or mixed varieties can be purified quickly by selecting again their best selfed lines.
• High Heritable Quality– desired traits once fixed are transmitted faithfully to next generation without segregation.
• Better Quality Control– uniform grain size, color, and texture help in industrial uses / processing.
• Simple and Low-Cost Method– doesn’t require hybridization or complex crossing; only careful plant selection & evaluation.
• Useful for Small Programs– suitable for regions or institutes with limited facilities / funds but need local variety improvement.
• Foundation for Seed Programs– forms base material for breeder, foundation and certified seed production.
• Reliable Research Material– because of uniform genotype, used in genetic & physiological experiments.
• Helps in Improving Landraces– turns heterogeneous local population into stable cultivar adapted to regional conditions.
• Less Risk of Segregation– since plants homozygous, no unwanted recombination occurs during seed multiplication.

Disadvantages of Pureline Selection

• Loss of Genetic Variation– after many selfing generations, genetic diversity almost gone, so adaptability reduced.
• Narrow Genetic Base– purelines can’t tolerate sudden climatic or disease changes well.
• Low Response to Selection– once line fixed, further selection inside it give no improvement.
• Time Consuming Process– normally 8–10 years needed for evaluation and release of a new pureline.
• Less Flexibility– hard to combine two or more useful traits since no crossing involved.
• Poor Adaptation – same line may fail in different locations due to lack of genetic buffer.
• Environmental Dependence– uniform genotype react differently under changing soil or climate; performance may drop.
• High Risk of Epidemic– when all plants same, one new pathogen can destroy whole crop quickly.
• Limited Scope for Heterosis– no hybrid vigor seen because plants homozygous.
• Not Suitable for Cross-Pollinated Crops– method works poorly for species like maize or sunflower.
• Economic Risk– uniform variety may give high yield in good years but big loss when conditions turn bad.
• Lack of Novelty – doesn’t generate new gene combinations, so breeding progress very slow compared to hybridization.

Achievements of Pureline Selection

The concept introduced by Johannsen (1903) proved that variation inside a self-pollinated crop is mostly environmental, not genetic — a key scientific turning point in plant breeding history.

Pureline selection gave foundation for all later breeding work on self-pollinated crops, especially for cereals and pulses.

Many early wheat and barley varieties in Europe and India were developed by this method — e.g., ‘Pb 11’, ‘Kalyan Sona’ traces part of their improvement to pureline isolation.

Rice improvement through selection of stable purelines from local landraces produced high-yielding lines still cultivated in some Asian regions.

This method helped define the term “variety” in genetic sense – a uniform, homozygous population derived from one individual.

Enhanced uniformity in agricultural production — industries benefited because grain quality became predictable.

Contributed to food security, especially in early 20th century when pureline wheat and barley improved yield consistency.

Provided baseline for hybrid and mutation breeding, since purelines became parental stock for new experiments.

Simplified seed certification programs; pureline varieties made quality control practical at field level.

Many research findings on heritability and environmental influence validated through pureline studies.

The concept spread quickly – adopted by breeding stations worldwide, forming core method of classical breeding for decades.

Still now, pureline selection remains achievement that shaped modern plant improvement philosophy.

Comparison Between Pureline Selection and Mass Selection